The present invention relates to an ink jet print head for discharging ink drops from ink outlets by use of thermal energy.
Description of the Related Art
Recently, in contrast with the wire dot printing methods, non-impact recording method is attracting interest because the recording noise level is negligible. In particular, an ink jet recording method is attractive as it permits high-speed recording on ordinary paper without the need of a deposition treatment on the paper side. In the field, therefore, aiming at an optimal ink discharge performance, various approaches have been made, with associated implementations.
In the ink jet recording method, a recording is effected with discharged droplets of recording liquid, called "ink" deposited on a recordable material. This method is categorized into several systems according to the manner in which the drops of recording liquid are formed.
FIG. 1 illustrates a bubble jet recording system as a conventional example. The conventional system includes a substrate 32 provided with a heating resistor 30, a channel plate member 36 for defining an ink supply path 34, and an orifice plate 40 formed with an orifice as an ink outlet 38 communicating with the ink supply path 34. The heating resistor 30 rapidly heats to vaporize a volume of ink supplied on a heating zone surrounding the resistor 30, causing ink bubbles 42 to grow, exerting pressures therearound so that an ink drop is discharged from the ink outlet 38, with trailing droplets 50, 52 as shown in FIG. 2.
Grown bubbles 42 become deflated as they are cooled by surrounding ink, and fade out with ink vapour therein condensed to be liquidated.
A consumed volume of ink by the discharge is supplemented from an ink pool through the ink supply path 34, due to capillary forces acting on an ink meniscus 44 retreating inside the ink outlet 38.
To permit a high-speed recording, it is desirable to repeat a discharge of an ink drop in a short period, supplementing at a high speed a volume of ink consumed during every discharge through the ink outlet 38.
In a conventional implementation, the diameter of the ink outlet 38 is reduced to have an increased capillary force, and the channel resistance of the ink supply path 34 is reduced.
Thus, ink is supplemented at an increased speed, and with an increased momentum, which causes, as shown in FIG. 1, an elongated ink pillar 46 to project from the ink outlet 38, before it deforms into an ink drop. In the deformation, the elongated ink pillar 46 is broken so that a leading upper portion is changed into a main drop 48 and a trailing lower portion is separated into a number of relatively large low-speed satellites 50, 52 such as in FIG. 2. Such satellites adversely affect the printing.
Moreover, as a volume of ink is supplemented with an increased momentum, as shown in FIG. 3, an ink meniscus 44 at a top end of the ink outlet 38 has an increased tendency to convex outside and concave inside of the outlet 38. The meniscus 44 thus vibrates with a reduced damping ratio. That is, the vibration of the meniscus 44 is not readily stopped.
As the ink discharge is repeated in a short period, a subsequent discharge occurs immediately after the supplement of ink, so that it may occur when the ink meniscus 44 starts convexing above the ink outlet. This causes an undesirable deformation of an ink drop and an undesirable development of low-speed satellites, resulting in a reduced quality of recording.
Further, some volume of ink may flood over a surface area around the ink outlet 38, causing an ink drop to be discharged in an oblique direction, or bubbles to be involved, stopping the discharge, with a reduced reliability of recording.
A probable solution to such problems may include entering subsequent discharge after a sufficient damping of vibration, which however is inconsistent with an intended high-speed recording.
The present invention has been achieved with such points in mind.